Reactions in two-dimensional state

An enzymatic hydrolysis reaction of a diglyceride, able to give spreading monolayers, was followed by surface pressure measurements as a function of the time. The present study reports the characterisation of 1,2-dicaprin (DCP) monolayers, as substrates of the reaction, by means of spreading isotherms at four temperatures, surface potential and ellipsometric/spectroscopic measurements. The results show that: (a) the hydrolysis reaction can take place only for definite values of surface pressure, corresponding to the condensed phase of the lipid film; (b) the reaction is of zero-order and it has an activation energy of about 1400 cal/moles; (c) the study of the inhibition of this reaction, by means of β-lactoglobulin (β-LG), shows that the inhibition does not derive from a direct interaction protein-enzyme, but the protein modifies the lipid substrate on which the enzyme acts.